Repair of aortic coarctation is sometimes associated with two hazardous postoperative complications; a severe exacerbation of the pre-existing systemic hypertension and mesenteric vasculitis. A sudden change in pressure and flow distal to the coarctation has been suggested as the initiator of these postoperative events, but laboratory assessment of the clinical situation has been hampered by the difficulty in creating an appropriate laboratory model and by accurate methods of measuring flow to various organs over a several day period. We have developed a successful method of producing aortic coarctation in young dogs by constructing the descending thoracic aorta with a tape tied over felt pads. After these animals have matured we will repair the coarctation and will perform chronic flow measurements by injecting radioactive microspheres via a catheter implanted in the left atrium. Flow to the myocardium, gut, kidney, and skeletal muscle will be assessed in these animals (unanesthetized) prior to repair, in the immediate postoperative period, and after postoperative equilibration occurs.